Deprecate Trainer.devices in favor of Trainer.num_devices and Trainer.device_ids

CHANGELOG.md

@@ -152,6 +152,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added support to explicitly specify the process group backend for parallel strategies ([#11745](https://github.com/PyTorchLightning/pytorch-lightning/pull/11745))
 
 
+- Added `device_ids` and `num_devices` property to `Trainer` ([#12151](https://github.com/PyTorchLightning/pytorch-lightning/pull/12151))
+
+
 ### Changed
 
 - Drop PyTorch 1.7 support ([#12191](https://github.com/PyTorchLightning/pytorch-lightning/pull/12191))
@@ -518,6 +521,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecated `ParallelPlugin.torch_distributed_backend` in favor of `DDPStrategy.process_group_backend` property ([#11745](https://github.com/PyTorchLightning/pytorch-lightning/pull/11745))
 
 
+- Deprecated `Trainer.devices` in favor of `Trainer.num_devices` and `Trainer.device_ids` ([#12151](https://github.com/PyTorchLightning/pytorch-lightning/pull/12151))
+
+
 ### Removed
 
 - Removed deprecated parameter `method` in `pytorch_lightning.utilities.model_helpers.is_overridden` ([#10507](https://github.com/PyTorchLightning/pytorch-lightning/pull/10507))

pytorch_lightning/trainer/trainer.py

@@ -2010,6 +2010,23 @@ def should_rank_save_checkpoint(self) -> bool:
     def num_nodes(self) -> int:
         return getattr(self.strategy, "num_nodes", 1)
 
+    @property
+    def device_ids(self) -> List[int]:
+        """List of device indexes per node."""
+        devices = getattr(self.strategy, "parallel_devices", [self.strategy.root_device])
+        device_ids = []
+        for idx, device in enumerate(devices):
+            if isinstance(device, torch.device):
+                device_ids.append(device.index or idx)
+            elif isinstance(device, int):
+                device_ids.append(device)
+        return device_ids
+
+    @property
+    def num_devices(self) -> int:
+        """Number of devices the trainer uses per node."""
+        return len(self.device_ids)
+
     @property
     def num_processes(self) -> int:
         return self._accelerator_connector.num_processes
@@ -2031,8 +2048,12 @@ def num_gpus(self) -> int:
         return self._accelerator_connector.num_gpus
 
     @property
-    def devices(self) -> Optional[Union[List[int], str, int]]:
-        return self._accelerator_connector.devices
+    def devices(self) -> int:
+        rank_zero_deprecation(
+            "`Trainer.devices` was deprecated in v1.6 and will be removed in v1.8."
+            " Please use `Trainer.num_devices` or `Trainer.device_ids` to get device information instead."
+        )
+        return self.num_devices
 
     @property
     def data_parallel_device_ids(self) -> Optional[List[int]]:

tests/accelerators/test_accelerator_connector.py

@@ -579,22 +579,22 @@ def test_validate_accelerator_and_devices():
 def test_set_devices_if_none_cpu():
 
     trainer = Trainer(accelerator="cpu", num_processes=3)
-    assert trainer.devices == 3
+    assert trainer.num_devices == 3
 
 
 @RunIf(min_gpus=2)
 def test_set_devices_if_none_gpu():
 
     trainer = Trainer(accelerator="gpu", gpus=2)
-    assert trainer.devices == 2
+    assert trainer.num_devices == 2
 
 
 def test_devices_with_cpu_only_supports_integer():
 
     with pytest.warns(UserWarning, match="The flag `devices` must be an int"):
         trainer = Trainer(accelerator="cpu", devices="1,3")
     assert isinstance(trainer.accelerator, CPUAccelerator)
-    assert trainer.devices == 1
+    assert trainer.num_devices == 1
 
 
 @pytest.mark.parametrize("training_type", ["ddp2", "dp"])
@@ -941,15 +941,15 @@ def test_unsupported_ipu_choice(mock_ipu_acc_avail, monkeypatch):
 @mock.patch("pytorch_lightning.utilities.imports._IPU_AVAILABLE", return_value=False)
 def test_devices_auto_choice_cpu(is_ipu_available_mock, is_tpu_available_mock, is_gpu_available_mock):
     trainer = Trainer(accelerator="auto", devices="auto")
-    assert trainer.devices == 1
+    assert trainer.num_devices == 1
     assert trainer.num_processes == 1
 
 
 @mock.patch("torch.cuda.is_available", return_value=True)
 @mock.patch("torch.cuda.device_count", return_value=2)
 def test_devices_auto_choice_gpu(is_gpu_available_mock, device_count_mock):
     trainer = Trainer(accelerator="auto", devices="auto")
-    assert trainer.devices == 2
+    assert trainer.num_devices == 2
     assert trainer.gpus == 2
 
 

tests/accelerators/test_ipu.py

@@ -400,7 +400,7 @@ def test_manual_poptorch_opts(tmpdir):
     dataloader = trainer.train_dataloader.loaders
     assert isinstance(dataloader, poptorch.DataLoader)
     assert dataloader.options == training_opts
-    assert trainer.devices > 1  # testing this only makes sense in a distributed setting
+    assert trainer.num_devices > 1  # testing this only makes sense in a distributed setting
     assert not isinstance(dataloader.sampler, DistributedSampler)
 
 
@@ -588,7 +588,7 @@ def test_accelerator_ipu_with_ipus_priority():
 def test_set_devices_if_none_ipu():
 
     trainer = Trainer(accelerator="ipu", ipus=8)
-    assert trainer.devices == 8
+    assert trainer.num_devices == 8
 
 
 @RunIf(ipu=True)
@@ -631,5 +631,5 @@ def test_poptorch_models_at_different_stages(tmpdir):
 @RunIf(ipu=True)
 def test_devices_auto_choice_ipu():
     trainer = Trainer(accelerator="auto", devices="auto")
-    assert trainer.devices == 4
+    assert trainer.num_devices == 4
     assert trainer.ipus == 4

tests/accelerators/test_tpu.py

@@ -94,14 +94,15 @@ def test_accelerator_cpu_with_tpu_cores_flag():
 
 
 @RunIf(tpu=True)
+@pl_multi_process_test
 @pytest.mark.parametrize(["accelerator", "devices"], [("auto", 8), ("auto", "auto"), ("tpu", None)])
 def test_accelerator_tpu(accelerator, devices):
     assert TPUAccelerator.is_available()
 
     trainer = Trainer(accelerator=accelerator, devices=devices)
     assert isinstance(trainer.accelerator, TPUAccelerator)
     assert isinstance(trainer.strategy, TPUSpawnStrategy)
-    assert trainer.devices == 8
+    assert trainer.num_devices == 8
     assert trainer.tpu_cores == 8
 
 
@@ -117,10 +118,10 @@ def test_accelerator_tpu_with_tpu_cores_priority():
 
 
 @RunIf(tpu=True)
+@pl_multi_process_test
 def test_set_devices_if_none_tpu():
-
     trainer = Trainer(accelerator="tpu", tpu_cores=8)
-    assert trainer.devices == 8
+    assert trainer.num_devices == 8
 
 
 @RunIf(tpu=True)
@@ -310,3 +311,21 @@ def test_mp_device_dataloader_attribute(_):
 def test_warning_if_tpus_not_used():
     with pytest.warns(UserWarning, match="TPU available but not used. Set `accelerator` and `devices`"):
         Trainer()
+
+
+@pytest.mark.skip(reason="TODO(@kaushikb11): Optimize TPU tests to avoid timeouts")
+@RunIf(tpu=True)
+@pytest.mark.parametrize(
+    ["devices", "expected_device_ids"],
+    [
+        (1, [0]),
+        (8, list(range(8))),
+        ("8", list(range(8))),
+        ([2], [2]),
+        ("2,", [2]),
+    ],
+)
+def test_trainer_config_device_ids(devices, expected_device_ids):
+    trainer = Trainer(accelerator="tpu", devices=devices)
+    assert trainer.device_ids == expected_device_ids
+    assert trainer.num_devices == len(expected_device_ids)

tests/deprecated_api/test_remove_1-8.py

@@ -878,3 +878,12 @@ def all_gather(self, tensor):
         match="ParallelStrategy.torch_distributed_backend was deprecated" " in v1.6 and will be removed in v1.8."
     ):
         strategy.torch_distributed_backend
+
+
+def test_trainer_config_device_ids():
+    trainer = Trainer(devices=2)
+    with pytest.deprecated_call(
+        match="`Trainer.devices` was deprecated in v1.6 and will be removed in v1.8."
+        " Please use `Trainer.num_devices` or `Trainer.device_ids` to get device information instead."
+    ):
+        trainer.devices == 2

tests/trainer/flags/test_env_vars.py

@@ -51,6 +51,6 @@ def test_passing_env_variables_defaults():
 def test_passing_env_variables_devices(cuda_available_mock, device_count_mock):
     """Testing overwriting trainer arguments."""
     trainer = Trainer()
-    assert trainer.devices == 2
+    assert trainer.num_devices == 2
     trainer = Trainer(accelerator="gpu", devices=1)
-    assert trainer.devices == 1
+    assert trainer.num_devices == 1

tests/trainer/test_trainer.py

@@ -30,6 +30,7 @@
 from torch.optim import SGD
 from torch.utils.data import DataLoader, IterableDataset
 
+import pytorch_lightning
 import tests.helpers.utils as tutils
 from pytorch_lightning import Callback, LightningDataModule, LightningModule, Trainer
 from pytorch_lightning.accelerators import CPUAccelerator, GPUAccelerator
@@ -2117,3 +2118,35 @@ def test_dataloaders_are_not_loaded_if_disabled_through_limit_batches(running_st
         else getattr(trainer, f"{dl_prefix}_dataloaders")
     )
     assert dl is None
+
+
+@pytest.mark.parametrize(
+    ["trainer_kwargs", "expected_device_ids"],
+    [
+        ({}, [0]),
+        ({"devices": 1}, [0]),
+        ({"devices": 1}, [0]),
+        ({"devices": "1"}, [0]),
+        ({"devices": 2}, [0, 1]),
+        ({"accelerator": "gpu", "devices": 1}, [0]),
+        ({"accelerator": "gpu", "devices": 2}, [0, 1]),
+        ({"accelerator": "gpu", "devices": "2"}, [0, 1]),
+        ({"accelerator": "gpu", "devices": [2]}, [2]),
+        ({"accelerator": "gpu", "devices": "2,"}, [2]),
+        ({"accelerator": "gpu", "devices": [0, 2]}, [0, 2]),
+        ({"accelerator": "gpu", "devices": "0, 2"}, [0, 2]),
+        ({"accelerator": "ipu", "devices": 1}, [0]),
+        ({"accelerator": "ipu", "devices": 2}, [0, 1]),
+    ],
+)
+def test_trainer_config_device_ids(monkeypatch, trainer_kwargs, expected_device_ids):
+    if trainer_kwargs.get("accelerator") == "gpu":
+        monkeypatch.setattr(torch.cuda, "is_available", lambda: True)
+        monkeypatch.setattr(torch.cuda, "device_count", lambda: 4)
+    elif trainer_kwargs.get("accelerator") == "ipu":
+        monkeypatch.setattr(pytorch_lightning.accelerators.ipu.IPUAccelerator, "is_available", lambda _: True)
+        monkeypatch.setattr(pytorch_lightning.strategies.ipu, "_IPU_AVAILABLE", lambda: True)
+
+    trainer = Trainer(**trainer_kwargs)
+    assert trainer.device_ids == expected_device_ids
+    assert trainer.num_devices == len(expected_device_ids)